After the cancellation of the N1 development in 1974, the Mars sample return mission had to be downsized to fit onto the much smaller Proton rocket. To make it possible, the mission was initially split among three Proton boosters...

5MN project had to be dramatically scaled down to fit into three Proton rockets.

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Doubts set in

Around 1973, after couple of years of efforts to design the Mars sample return mission, the Scientific and Technical Council, NTS, reviewed the 5M project and identified two major obstacles for the program. First of all, the developers could not guarantee the bacteriological security of the mission. For example, in case of a parachute failure during the return to Earth, the capsule could spew soil samples along with hypothetical Martian bacteria in the Earth's biosphere with unpredictable consequences.

Secondly, and perhaps, decisively, there was little hope that many of the key systems on the spacecraft, first of all its avionics, could survive mission lasting nearly three years.

Still, Sergei Afanasiev, the influential Minister of the General Machine-building, MOM, which oversaw the rocket industry, saw major advantages in the project, probably both in scientific and political terms. Clearly, returning soil samples from Mars would be an unmatched technological achievement. Convinced that biological safety problems could be resolved, Afanasiev tried to persuade the head of the Soviet planetary program Georgy Babakin to tackle engineering problems, but, to not avail. More than anyone else, Babakin understood the major technical hurdles facing the 5M project. Afanasiev then turned to a key engineer at NPO Lavochkin Vladimir Perminov, promising him all the necessary support if he was to take on the project, but, by his own recollection, Perminov also felt unconvinced.

Retailoring the project from N1 to Proton

Minister Afanasiev returned to the idea of a Mars sample return mission in 1974, in the wake of the Mars-73 campaign, which saw four Soviet launches to Mars. Despite the relatively limited scientific success of the missions, they gave considerable experience to the developers of future Mars probes. At NPO Lavochkin, Perminov then attempted to tackle the task of a Mars sample return mission.

By that time, the development of the N1 rocket had been canceled after four failed launches, but the Proton rocket had matured enough to become the carrier for the entire Soviet planetary exploration program.

To fit the 5M spacecraft onto the smaller Proton rocket, the mission was initially split between three rockets. Two of the components were based on the Block-D upper stage upgraded for a rendezvous in the Earth's orbit. One would carry the 8,500-kilogram 5M spacecraft with the lander and the Mars ascent stage, while another would launch with the full complement of propellant for escaping the Earth's orbit. Finally, the third rocket would launch the Earth-return vehicle.

After taking samples on the surface of the Red Planet, the 2,000-kilogram Mars ascent stage would blast off from its lander and enter Martian orbit, where it would have to link up with the Earth-return vehicle. The capsule with soil would be reloaded from the Martian ascent stage onto the Earth return vehicle, which would then escape the Martian orbit on its way to Earth. On approach to Earth, the spacecraft would enter the Earth's orbit, where it would be intercepted by a manned spacecraft, which would subsequently return the tiny capsule with the precious samples back to Earth to avoid risky parachute descent and potential contamination of our planet's biosphere with the Martian bacteria.

As a dress-rehearsal for the complex soil-return mission, the 4M Mars rover would make a one-way trip to Mars before the launch of the 5M mission.

However, the whole scheme of the 5M project looked very complex and totally unreliable. In desperation, Soviet engineers even looked at NASA's Saturn-5 rocket, which could certainly carry enough payload to implement the Mars sample return mission in a single shot, with the biological security of the mission fully ensured. However the idea was politically unrealistic, not to mention the economics and the fact that the Saturn-5 itself had made its last launch in 1973.

Perminov presented the results of the studies on the 5M project to the chief designer Kryukov, along with a pessimistic assessment of the probability of success. After some discussions, Perminov proposed to put off the project until better days and when Kryukov disagreed, Perminov resigned from further participation. The leadership over the project was then transferred to V. P. Panteleev. (633)